the bomber or bombers still not found it is a city very much on edge. Beached you have security and high alert matched here in new york and other major cities across the country. Abc's dan harris has more on all this from boston. Good morning, dan. Reporter: Hey, george, good morning to you. The city is trying to edge way back toward normalcy but that's tricky to do. You have 12 blocks of the normally bustling downtown shut down as a massive crime scene. Second of all, people here are justifiably still a little bit nervous and not just in boston, this is happening all over the country. The american people refuse to be terrorized. Reporter: When president obama asked us to stay vigilant in the wake of the attacks, he may not have foreseen this. Bomb-sniffing dogs and robots working overtime. Americans seeing something and saying something in droves. You feel safer by seeing it but brings it to the forefront of what could happen. Reporter: A rash of suspicious packages called in to 911 tuesday. They located an abandoned box in the trash can that's suspicious in nature. It has wires coming out it. Reporter: A bomb-sniffing dog took out this hair drier. Police in new york city fielded 77 such reports in less than 24 hours. Three times the norm. It would be easier if we just did pay attention, but if yesterday doesn't refresh your memory, I don't know what would. Reporter: The epicenter of the jitters quite justifiably boston where streets this morning are filled with armored vehicles, heavily armed cops and the national guard. At logan airport officials removed all passengers from a u.S. Air flight because of concerns over a strange noise. AT NEW YORK's LaGuardia, thousands of passengers were held outside after calls came in about exposed wires in a light fixture and at landmarks in major cities all over america law enforcement keeping anything but a low profile. I am not in the hope for the best business. I am in the plan for the worst business. Reporter: Meanwhile, in 15 cities around america they are planning to hold marathons of their own within the next week. All of those places now having to think about security in a whole new way.

This transcript has been automatically generated and may not be 100% accurate.

Stories of the 3 Killed at Boston Marathon

An 8-year-old boy, a restaurant manager and a Chinese graduate student died in the attack.

The Hunt for the Boston Marathon Bomber

Former counterterrorism head Dick Clarke discusses the marathon bombing investigation.

{"id":18976674,"title":"Boston on Edge After Marathon Bombing","duration":"2:15","description":"Security has been beefed up with the bomber still on the loose.","section":"GMA","mediaType":"Default"}